Sensor for Fitness Equipment

ABSTRACT

An exercise machine has a rotating joint with an accelerometer mounted on the rotating joint. A microprocessor converts the signal from the accelerometer into a distance measurement based on the machine characteristics.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority benefit of U.S. Provisional Patent Application No. 61/483,395 filed on May 6, 2011, which is incorporated herein by reference.

BACKGROUND OF INVENTION

There is a need for a sensor for fitness equipment that is economical and that can be used with both weight stack and hydraulic fitness machines.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is illustrated in the drawings in which like reference characters designate the same or similar parts throughout the figures of which:

FIG. 1 is a schematic diagram showing an accelerometer mounted on a shaft;

FIG. 2 is a system block diagram for the present invention; and,

FIG. 3 is a schematic of the sensor design.

DETAILED DESCRIPTION OF THE INVENTION

In both hydraulic and weight stack systems, the user pulls and pushes a lever backwards and forwards. This lever is connected, through some form of mechanism, to a resistance element, either a hydraulic cylinder or by a belt or cable to a stack of weights that move vertically. Both hydraulic and weight stack machines use a mechanism that has some form of a rotational joint. Thus an accelerometer and an 8-bit microprocessor can be configured to give a distance measurement for all types of equipment In the majority of cases, the axis of the joint is parallel or at some angle to the ground. In cases where this joint is normal to the ground, the lever coming off of the joint is at an angle to the ground. This feature can be used by a single sensor that uses an accelerometer to measure the force relative to gravity and thus the angle of the joint as it moves. With a knowledge of the mechanism to which the joint is attached, the distance moved by the resistive element (cylinder or weights) can be calculated. From this distance information, a microprocessor can calculate a variety of factors such as stroke count, stroke length and velocity etc. This data, over time, is then used to give feedback to the user and can be used to calculate energy (calories) and power. The machine characteristics for hydraulic exercise machines are set forth in greater detail in U.S. Pat. No. 7,914,425 entitled “Hydraulic Exercise Machine System and Methods Thereof” which is assigned to the assignee of this invention and which is incorporated herein by reference. A weight-stack exercise machine comprises a stack of weights that is lifted as the person exercising on the exercise machine moves one or more physical components of the exercise machine. The sensing system senses a distance that the weights have been displaced or a velocity or acceleration of the weights or other physical component of the exercise machine. From this sensed information, the computer system may determine user performance data. The machine characteristics of a weight-stack exercise machine are discussed in greater detail in U.S. Pat. No. 7,846,067 entitled “Fatigue and Consistency in Exercising” which is assigned to the assignee of the present invention and is incorporated herein by reference.

A typical application is shown in FIG. 1, where the accelerometer 10 (FIG. 2) is mounted in an enclosure 28 on the top of a rotational joint 13. A bar 14 may be attached at the joint 13. The bar 14 may be rotated by the action of the user. Either the Z-axis 16 or X-axis 19 can be used to determine the angle of rotation, even when the device is mounted at 90 degrees to the orientation shown. Note that in this application the Y-axis is redundant.

The application may use a dual axis accelerometer, however this would then rely on a single axis being used to measure the angle, and the sensitivity and accuracy are reduced. Therefore it is preferable for a 3-axis accelerometer to be used whereby any of the three axes can be used to measure the angle. The measurement of tilt requires an accelerometer to measure +/−1.2 g with reasonable accuracy.

An accelerometer uses the force of gravity as an input vector to determine the orientation of an object in space. An accelerometer is most sensitive to tilt when its sensitive axis is perpendicular to the force of gravity, i.e., parallel to the earth's surface. At this orientation, its sensitivity to changes in tilt is highest. When the accelerometer is oriented on axis to gravity, i.e., near its +1 g or −1 g reading, the change in output acceleration per degree of tilt is negligible. When the accelerometer is perpendicular to gravity it output changes nearly 17.5 mg per degree of tilt. At forty-five degrees, its output changes at only 12.2 mg per degree and resolution declines. When the accelerometer is oriented so both its X and Y axes are parallel to the earth's surface, it can be used as a two-axis tilt sensor with a roll axis and a pitch axis. Once the output signal from the accelerometer has been converted to an acceleration that varies between −1 g and +1 g, the output tilt in degrees is calculated as follows:

Pitch=ASin(A _(X)/1 g)

Roll=ASin (A _(Y)/1 g)

The sensor 22 may be constructed as a single-sided printed circuit board (PCB) 25 with a small footprint. The PCB 25 is mounted into a plastic enclosure 28 that can be attached to the machine joint 13 using double sided tape or VELCRO fasteners. The sensor 22 is connected to an interface box with a 6 foot cable 34, with strain relief at the enclosure and terminated in a green 4-pin DIN plug. A system block diagram is shown in FIG. 2.

The microprocessor 37 has the following functions: 1) sample and filter accelerometer's signal at 100 Hz; 2) convert accelerometer signal to an angle; 3) convert angle to a distance according to a program based on the machine characteristics; 4) output the distance measurement as an analog or digital signal; and 5) calibration as discussed below.

The sensor 22 may be powered by regulated 5V DC power supply 24. The device output 40 is an analog output up to 5V (i.e. Vcc). Generally the output will be scaled zero to 3V, based on the application and to ensure that the output 40 is not trying to be driven beyond the available power supply. The analog output is preferably capable of driving at least twelve feet of cabling.

In some cases it is advantageous to have a digital output, therefore an RS232 port is provided for this purpose.

The PCB 22 is mounted in a small low-profile plastic enclosure 28 that is shaped to fit the machine joint 13. It is common for machines to have joint diameters of one to two inches and flat. The enclosure 28 is designed so that the base is curved to fit these sizes, through an interchangeable base or adaptor piece. The sensor 22 is attached to the machine joint 13 using double sided foam tape or VELCRO fasteners.

For the device to be used as a sensor, it is zeroed out and placed in an orientation where it is most effective. The intent is for the sensor 22 to be installed by the owner or operator of a fitness club. Therefore, a setup and calibration process indicates to the user the optimal alignment and sets a zero point. The calibration process is as follows: 1) with the sensor 22 plugged in and powered up, the installer presses a calibration button 43 to place the sensor 22 into the calibration mode; 2) an LED display 44 flashes slowly. When the sensor 22 is held horizontally or vertically the flash speed increases. This indicates to the installer that the sensor 22 is aligned to within five degrees or normal; 3) the sensor 22 is fixed to the rotational joint 13; 4) the installer presses the calibration button 43 a second time. This causes the microprocessor 37 to sample the data and set a zero point; 5) the LED display 44 then flashes intermittently to indicate that the sensor is functioning normally.

The sensor 22 is installed at a predetermined position on the weight stack or hydraulic fitness equipment.

While the invention has been described in connection with certain embodiments, it is not intended to limit the scope of the invention to the particular forms set forth, but on the contrary, it is intended to cover such alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention. 

1. An exercise machine, comprising: a rotating joint; an accelerometer mounted on the rotating joint; and, a microprocessor for converting a signal from the accelerometer into a distance measurement based on the characteristics of the machine.
 2. The exercise machine of claim 1, wherein the accelerometer is a three-axis accelerometer.
 3. The exercise machine of claim 1, wherein the exercise machine is a hydraulic exercise machine.
 4. The exercise machine of claim 1, wherein the exercise machine is a weight stack machine.
 5. The exercise machine of claim 1, wherein the microprocessor converts the signal from the accelerometer into an angle.
 6. The exercise machine of claim 1, wherein the microprocessor includes an output for the distance measurement.
 7. The exercise machine of claim 6, wherein the distance measurement is an analog signal.
 8. The exercise machine of claim 6, wherein the distance measurement is a digital signal.
 9. The exercise machine of claim 1, further comprising a power source.
 10. The exercise machine of claim 9, wherein the power source is 5V DC.
 11. The exercise machine of claim 1, further comprising means for mounting the accelerometer onto the rotating joint.
 12. The exercise machine of claim 1, wherein the mounting means comprises a hook and loop fastener.
 13. The exercise machine of claim 1, wherein the mounting means comprises an adhesive.
 14. The exercise machine of claim 1, wherein the accelerometer and the microprocessor are mounted on a printed circuit board.
 15. The exercise machine of claim 1, further comprising an LED display.
 16. An exercise machine, comprising: a rotating joint; an accelerometer mounted on the rotating joint, the accelerometer producing a signal corresponding to the position of the rotating joint; and, means for converting the accelerometer signal into a distance based on the characteristics of the machine.
 17. The exercise machine of claim 16, wherein the accelerometer is a three-axis accelerometer.
 18. The exercise machine of claim 16, wherein the exercise machine is a hydraulic machine.
 19. The exercise machine of claim 16, wherein the exercise machine is a weight stack machine.
 20. The exercise machine of claim 16, wherein the converting means converts the signal into an angle. 